Large electric machines present unique engineering challenges. For example, the operational cooling of electrical generators used in large fossil and nuclear power generation plants is a particularly interesting problem. Of the many parts requiring cooling in large electric generators, cooling the stator bars is of significant importance. The stator bars carry most of the electrical power generated and therefore heat up very quickly due to, for example, general ohmic losses. I2R losses and eddy current losses. For many years, stator bars have been water cooled by circulating ultra-pure deionized water therethrough. This water travels out of the generators to cooling arrays where heat is removed, and is then recirculated to the generators in a closed loop system. One example of such a water cooled generator is a General Electric Corp. model 4A4W2 electric generator.
Stator bars conventionally comprise multiple strands. These strands are generally rectangular and are composed of an electrically conductive material such as, for example, copper. They are grouped together to form rectangular stator bars. The strands are individually insulated from each other within a stator bar to reduce eddy currents and associated losses. However, the strands of the stator bars are typically brazed together at their ends to facilitate electrical connection and liquid seal therebetween. To provide cooling, at least several strands within the stator bar are hollowed such that cooling water may pass therethrough.
Since the stator bars carry most of the electrical power in generators, electrical connection thereto is necessary to extract electrical power therefrom. Further, a facility for introducing and removing cooling water from each stator bar is necessary. The traditional device for simultaneously providing these-electrical and fluidic functions is a single piece electrical and fluidic connector shown, for example, in FIG. 1 as connector 11. This single piece connector provides: 1) electrical connection from a stator bar 19, through its own copper body (i.e., connector 11) and through a set of copper leaves 17 (and/or copper piping in, for example, a series loop system) to an electrical bus in the generator; and 2) fluidic connection from the water carrying strands in stator bar 19, through an inner chamber to a fluidic connector 15 where the water is passed to a hose for transfer.
Water cooling of stator bars is not without problems, however. One particularly serious problem is water leakage. Due to the high volume of water passing through the stator bars, even a small leak can lead to a large volume of water entering areas of the generator in which water is undesirable. This can eventually lead to a catastrophic failure of the generator comprising, for example, a ground fault. Furthermore, leaks are very often hard to find because the stator bars are buried within large amounts of insulation deep within the electrical generator.
The conventional electrical and fluidic connector 11 discussed hereinabove has a propensity towards water leakage. Further, once a single water leak occurs, operational experience has shown a tendency toward the development of additional water leaks which are known to occur at several regions associated with the conventional connector 11. As one example, water leakage may occur at the interface between the stator bar 19 and the connector 11. This is due to the structure of the clip and associated assembly method. To explain, during factory assembly of the generator, the individual strands composing the stator bar are inserted into an opening 20 within the connector 11. The strands are then brazed to the connector 11 by a worker who accesses the internal brazed areas through a small window in the connector (the window is shown covered by plate 13). This is a difficult process as space within the connector 11 and the access window is limited. In fact, the window is so small that a worker will typically rely on dental mirrors and other ad-hoc brazing means to view the brazed connection being created. Thus, poor brazed connections that leak water may result. After brazing of the connector to the stator bar is completed, the window is closed by brazing a copper plate 13 thereover. This window and associated plate 13 provide yet another opportunity for water leakage. Thus, inherent in the conventional single piece electrical and fluidic connector are multiple connections that are prone to damaging water leakage.
The conventional electrical and fluidic connector and associated assembly techniques have a further disadvantage. Specifically, there is no way to easily replace a faulty connector while the associated stator bar is still within the generator. Therefore, a complete disassembly of the generator is conventionally recommended to replace a leaky connector. Of course, this is very expensive and highly undesirable.
The present invention is directed toward providing solutions for the above-noted problems.